Slush-ice berms on the west coast of Alaska: Development of a
conceptual model of formation based on input from and work with local
observers in Shaktoolik, Gambell and Shishmaref, Alaska
by
Laura Eerkes-Medrano
B.A., Universidad Nacional Autonoma de Mexico, 1983 M.Sc., Universidad Nacional Autonoma de Mexico, 1988
A Dissertation Submitted in Partial Fulfillment of the Requirements for the Degree of
DOCTOR OF PHILOSOPHY
in the Department of Geography
©Laura Eerkes-Medrano, 2017 University of Victoria
All rights reserved. This dissertation may not be reproduced in whole or in part, by photocopy or other means, without the permission of the author.
ii
Supervisory Committee
Slush-ice berms on the west coast of Alaska: Development of a conceptual model
of formation based on input from and work with local observers in
Shaktoolik, Gambell and Shishmaref, Alaska
by
Laura Eerkes-Medrano
B.A., Universidad Nacional Autonoma de Mexico, 1983 M.Sc., Universidad Nacional Autonoma de Mexico, 1988
Supervisory Committee
Dr. David Atkinson (Department of Geography) Supervisor
Dr. Johannes Feddema (Department of Geography) Departmental Member
Dr. Henry Huntington (Huntington Consulting) Additional Member
iii
Abstract
Supervisory Committee
Dr. David Atkinson (Department of Geography) Supervisor
Dr. Johannes Feddema (Department of Geography) Departmental Member
Dr. Henry Huntington (Huntington Consulting) Additional Member
Bering Sea storms regularly bring adverse environmental conditions, including
large waves and storm surges of up to 4 m, to the west coast of Alaska. These conditions
can cause flooding, erosion and other damage that affects marine subsistence activities and
infrastructure in the low-lying coastal communities. Storm impacts also include interactions
with sea ice in various states: large floes, shore-fast ice, the acceleration of sea-ice formation
in frazil or slush state, and the formation of slush-ice berms. Slush-ice berms are
accumulations of slush ice that develop under the right wind, water level, water and air
temperature, and snow conditions. During a strong wind event, large amounts of slush may
be formed and pushed onto the shore, where the slush can accumulate, solidify and protect
communities from flooding and erosion. Slush ice berms can also be problematic, restricting
access to the coast and presenting other hazards. Residents of Shishmaref and Shaktoolik,
communities on the west coast of Alaska, observed the formation of slush-ice berms during
iv
communities, and it would be useful to develop the capacity to predict their occurrence.
However, scientific work has not been conducted on this phenomenon, with the result that
a physical conceptual model describing the formation of slush-ice berms does not exist. In
recognition of this need, a project thesis was designed, and had as its main objective to
identify and document the environmental and synoptic weather conditions that lead to these
types of events, and to develop a descriptive physical conceptual model of slush-ice berm
formation. A key to this work was the engagement of traditional knowledge holders and
local observers to gather data and information about slush ice and slush-ice berm formation,
along with the specific dates when these events took place. This dissertation is organized
around three major elements: development of a conceptual model of slush-ice berm
formation; presenting the traditional knowledge gathered that led to the development of this
model; and documenting the methods and tools used to engage traditional knowledge
holders and local observers in this process. In this dissertation, the knowledge from
traditional knowledge holders on slush ice formation is presented in the context of feeding
into a physical scientific process – specifically, developing a descriptive physical
conceptual model of slush-ice berm formation. It is expected that this type of research will
contribute to slush-ice berm forecasting which would aid communities’ safety by improving
v
Table of Contents
Supervisory Committee ... ii
Abstract.. ... iii
Table of Contents ... v
List of Tables ... ix
List of Figures ... x
Acknowledgements ... xiii
Dedication ... xv
1
Introduction ... 1
1.1 Research Motivation ...92
Slush-ice berm formation on the west coast of Alaska ... 13
2.1 Article information ...13
2.1.1 Authors’ names and affiliations ... 13
2.1.2 Author’s and coauthors’contributions ... 14
2.2 Abstract ...14
2.3 Introduction ...16
2.4 Methods ...18
2.4.1 Study sites ... 19
vi
2.5.1 Types of Berms ... 23
2.6 Conclusion ...35
2.7 Acknowledgements ...37
3
Inupiaq and Siberian Yupik perspectives on slush-ice formation
on the west coast of Alaska ... 49
3.1 Article information ...49
3.1.1 Authors’ names and affiliations ... 49
3.1.2 Author’s and coauthors’ contributions ... 49
3.2 Abstract ...50
3.3 Introduction ...52
3.4 Methods ...59
3.5 Results and Discussion ...59
3.5.1 Slush-Ice and Slush-Ice Berm Formation Processes ... 60
3.5.2 Factors Contributing to Slush-Ice and Slush-Ice Berm Formation... 64
3.5.3 Types of Berms ... 67
3.5.4 Slush ice berm formation mechanisms ... 74
3.5.5 Advantages and Disadvantages from a sea-ice services perspective ... 77
vii
4
Engaging community and stakeholders in slush-ice berm
formation and impactful weather events research in Alaska, USA: A
community-centered and feedback-based adaptive approach ... 87
4.1 Article information ...87
4.1.1 Authors’ names and affiliations ... 87
4.1.2 Author’s and coauthors’ contributions ... 87
4.2 Abstract ...87
4.3 Introduction ...88
4.3.1 Preparatory work – Become community focused ... 94
4.3.2 Inviting communities ... 96
4.3.3 Discussing the Project ... 99
4.3.4 Interviewing methods ... 101
4.3.5 Site Visits ... 109
4.3.6 Second site visits ... 120
4.3.7 After the Project ... 125
4.4 Discussion ...125
4.4.1 Issues encountered – Before Project Commencement ... 126
4.4.2 Issues encountered – During Project Delivery ... 129
4.5 Conclusions ...137
viii
5.1 Main research results ...142
5.2 Conclusion ...147
5.3 Future work ...148
ix
List of Tables
Table 4.1 Cross-cultural communication. ... 105
Table 4.2 Inupiat and American values. ... 106
x
List of Figures
Figure 1.1 Shishmaref: Abandoned house sits on the beach after sliding off during the 2005
fall storm. Credit: Diana Haecker/AP ...11
Figure 1.2 Shaktoolik: Old power house. ...11
Figure 1.3 Shaktoolik: Concerns about drinking water quality. ... 12
Figure 1.4 Gambell: Airstrip. ... 12
Figure 2.1 Region of study. ... 38
Figure 2.2 Two in-situ slush-ice berms. ... 39
Figure 2.3 Surface winds (10m height) associated with the in situ slush-ice berm event of 10 November 2012 at Wales, Alaska. ... 40
Figure 2.4 Sea level pressure associated with the in situ slush-ice berm event of 10 November 2012 at Wales, Alaska. ... 40
Figure 2.5 Surface air temperature (2 m height) associated with the in situ slush-ice berm event of 10 November 2012 at Wales, Alaska. ... 41
Figure 2.6 Advective slush-ice berm with ice boulders pushed against a deep beach in the old part of town. ... 42
Figure 2.7 Advective slush-ice berm. ... 43
Figure 2.8 Sea level pressure associated with the advective slush-ice berm event of 11 November 2009 at Shaktoolik, Alaska. ... 43
Figure 2.9 : Sea level pressure associated with the advective slush-ice berm event of 9 November 2011 at Shaktoolik, Alaska. ... 44
xi
Figure 2.10 Surface winds (10m height) associated with the advective slush-ice
berm event of 11 November 2009 at Shaktoolik, Alaska. Small arrows indicate the direction
of the wind. ... 44
Figure 2.11 Surface winds (10m height) associated with the advective slush-ice
berm event of 9 November 2011 at Shaktoolik, Alaska. Small arrows indicate the direction
of the wind. ... 45
Figure 2.12 Surface air temperature (2 m height) associated with the advective
slush-ice berm event of 11 November 2009 at Shaktoolik, Alaska. ... 45
Figure 2.13 Surface air temperature (2 m height) associated with the advective
slush-ice berm event of 9 November 2011 at Shaktoolik, Alaska. ... 46
Figure 2.14 Surface air temperature (2 m height) associated with the storm event
that did not result in a berm, 9 November 2013 at Shaktoolik, Alaska. ... 46
Figure 2.15 Sea level pressure associated with the storm event that did not result in
a berm, 9 November 2013 at Shaktoolik, Alaska. ... 47
Figure 2.16 General taxonomy of slush-ice berm features. ... 48
Figure 3.1 Region of study. ... 82
Figure 3.2 The shallow areas around Cape Denbigh act as a hook for the slush to
accumulate. ... 83
Figure 3.3 Two in-situ slush-ice berms at Shaktoolik, November 2013. ... 83
Figure 3.4 Advective slush-ice berm in front of the new town of Shaktoolik,
November 2009. ... 84
xii
Figure 3.6 Ice boulders on top of the slush-ice berm in the old town of Shaktoolik.
... 85
Figure 3.7 Ice boulders. ... 86
Figure 3.8 Shoreline erosion. ... 86
Figure 4.1 Region of study. ... 141
xiii
Acknowledgements
I would like to express my special appreciation and thanks to my supervisor
Professor Dr. David Atkinson. You have been a great supervisor! Thank you for encouraging
my research and supporting me during this project. I value that you believe in your students
more than they believe in themselves. My most sincere thanks go to my committee
members, Dr. Johannes Feddema and Dr. Henry Huntington. It has been a great experience
to learn from such great scholars and kind people. I also want to thank Olivia Lee for her
invaluable comments and to Hajo Eicken for his support and invaluable advice. I am also
very grateful to the residents of Gambell, Shaktoolik, and Shishmaref who welcomed me
in their villages and homes, and to the Tribal Councils for their support to conduct this project.
This dissertation was funded by the Western Alaska Landscape Conservation
Cooperative (WALCC) and the National Oceanic and Atmospheric Administration
(NOAA) to conduct a study based on work with community observers to develop a
conceptual model of slush-ice berm formation and to identify the impacts of storms and
adverse weather on community activities and infrastructure. Funding support by the
National Science Foundation of the SIZONet project is gratefully acknowledged. I
appreciate the important contributions by community-based ice observers and the Exchange
of Local Knowledge of the Arctic in the completion of this work.
Many thanks to my lab colleagues Norman, Katherine, Vida, Wayne, Chris, Adam,
xiv
Marjorie, you are like a family to me. To my family in Mexico, Canada, and Europe,
specially my mom and Dafne. It has been fun sharing this experience with you. Many
xv
Dedication
To John Eerkes-Medrano, for your love and support. You left way too soon but the
1
1 Introduction
The coast of western Alaska extends for over 1,200 km from north to south, from
Wainwright to Bristol Bay. This region is characterized by permafrost-dominated tundra
and river deltas (Terenzi, 2014). It has an abundance of salmon runs, seabirds and waterfowl
in the coastal areas and caribou, moose, bears and wolves on land. This area also includes
some threatened species such as sea otters and walruses (WALCC, 2016). Five native
groups inhabit this area: Unangax or Aleuts, Alutiiq or Pacific Eskimo, Central Yupik or
Southwestern Eskimo, Siberian Yupik or Bering Sea Eskimo and Inupiaq or Northern
Eskimo (GAO, 2009). This region is sparsely populated. Residents live in villages generally
with a current population of a couple of hundred people, that were originally inhabited by
their ancestors. They practice subsistence activities including fishing, hunting and gathering
of plants (GAO, 2009). Most communities have basic infrastructure, including school,
health clinic, store, church, post office, washateria, and city and tribal offices (GAO, 2009).
They are typically situated in low-lying, flat areas such as sandspits, river deltas, and barrier
islands. These locations were selected to meet subsistence needs, including fishing and
hunting and to build schools – a requirement imposed on them in the 1920s by the federal
Bureau of Indian Affairs (Bearded, T. 2008; USACE, 2008b; Marino, 2012). Western
Alaska is not accessible by road, so the locations for villages had to be accesible for barges
to navigate and offload school building materials. The transportation and
cultural/subsistence advantages offered by these locations are offset by the disadvantage of
being particularly vulnerable to storm surge impacts such as flooding and erosion. These
2 and sea ice retreats as a result of global climate change (McCabe et al., 2001; Terenzi et al.,
2014).
Global climate change in arctic regions shows a trend of generally increasing air
temperature over the 100-year period 1905–2006 that is almost twice the global average
change of 0.74 degrees Celsius (IPCC, 2007). Since the 1960s and 1970s, the average
temperature increase in arctic regions has been 1°C to 2°C, and this trend is expected to
continue (Anisimov et al., 2007). At the same time, and consistent with this warming, sea
ice in arctic regions has shown a decrease in extent, thickness and length of season (Vihma,
2014). In the Pacific Arctic region, Eicken and Mahoney (2014) indicate that over the past
three decades the length of the ice season has decreased by about a month.
In the northern part of the Bering Sea basin, sea ice normally forms in situ, along
the coast, in October and November, when cold northeasterly winds from arctic
high-pressure systems dominate the region, driving this ice towards the south and southwest
portion of the Seward Peninsula and St. Lawrence Island (Pease, Schoenberg and Overland,
1982). This ice advance can be interrupted by low-pressure systems that move into the
Bering Sea, bringing moist warm air with southerly wind. Any increase in frequency of
cyclonic activity and westerly cyclone tracks due to global warming could reduce the total
duration of northeasterly winds, and consequently of the ice growth, during the fall storm
season (Overland and Pease, 1982).
A reduction in the extent and thickness of shore-fast ice during the storm season
leaves the communities on the coast of Alaska more vulnerable to destructive waves and
storm-related impacts. Atkinson et al. (2011) describe an incidence of severe damage to a
3 formed on the structure’s wharf facility. Sea ice can also provide protection to communities
in different ways. Shore-fast ice armours the coast, increasing its resistance to erosion
(Eicken et al., 2009; Atkinson et al., 2011), and large pieces of floating ice can dampen
wave energy and mitigate the transfer of wind energy into the water. However, as shore-fast
ice becomes thinner, it is more prone to melting, deforming and disappearing (Vihma,
2014), and its damping effect on wave action is reduced. Less shore-fast ice results in winds
propagating longer distances over the water (longer fetch) creating higher amplitude waves
during the fall storm season (Atkinson, 2005; Francis and Atkinson, 2012).
Storms that reach western Alaska and the Bering Sea have usually originated and
intensified in the western North Pacific, east of Japan, over the warm western boundary of
the Kuroshio Current (Serreze, 1995; McCabe et al., 2001; Rodionov, 2007; Mesquita et
al., 2010). This is one of the most active storm tracks in the northern hemisphere. Storms
travel northeastward and develop into mature cyclones near the international dateline,
which is also the centre of the Aleutian Low. Most of these storms continue eastward into
the Gulf of Alaska or the eastern North Pacific, where their peak potential slowly weakens;
some others travel northward into the seas off western Alaska (Mesquita et al., 2010).
Storms can stall or remain stationary for a few days, resulting in moderate to strong winds
blowing from the same direction for extended periods of time (Rodionov, 2007). However,
these storms can also intensify further in the fall due to the temperature gradient between
the cold Siberian continental air mass and the relatively warm ocean air over the Bering Sea
(Rodionov, 2007). The resultant strong winds of long duration, combined with long
open-water fetches, generate large waves that can reach up to 8 m and drive open-water-level surges of
4 can cause significant negative impacts to the coastal zone (Chapman et al., 2009; Terenzi et
al., 2014; Erikson et al., 2015).
Atkinson (2005) outlines geomorphological, ecological and infrastructure impacts
on coastal arctic regions as a result of storm-induced waves. Such impacts were evident in
Shaktoolik, Shishmaref, and Gambell and provided a rationale for selecting these
communities for the project. Houses in Shishmaref have been relocated as a result of storm
impacts in 2005 (Figure 1.1). In Shaktoolik, electrical power lines were left exposed as a
result of coastal erosion during the 2013 storm (Figure 1.2), and there were concerns about
salt water contamination of the town’s drinking supply if the waves reached the river, which
supplies the town’s drinking water (Figure 1.3). In Gambell, during the 2013 storm, the
waves carried the gravel from the beach onto the airstrip, forcing the town to close the
airport, the community’s only means of year-round access to the mainland, leaving the town
isolated in case of emergency (Figure 1.4).
When sea-ice is in the early stages of formation, frazil or slush ice can be produced
in large quantities and driven by storm winds onto the shore, where it piles up in the
nearshore area. If this slush-ice accumulation has an opportunity to consolidate through
in-situ freezing, it may form solid structures that can greatly limit the adverse impact of surges,
as has been witnessed by local ice experts and residents in communities such as Unalakleet,
Golovin, Shishmaref and Wales (Eicken, 2010; Eicken et al., 2014). More recently, in 2009,
and 2011, storms threatened Shaktoolik and other communities at the eastern end of Norton
Sound with floods from the anticipated storm surges. However, slush ice was driven ashore,
solidified and formed a natural defensive barrier (a “berm”) that mitigated the impact of
5 Weather Service pers. comm. 2009). Similar findings have been reported for the Bering
Strait region (Eicken et al., 2014). These types of occurrences prompted Atkinson and
Eicken to apply for funding to investigate the weather and sea-ice conditions that lead to
berm formations. Although slush-ice berms can protect communities from storm impacts,
once they have solidified they can also impede travel and access to the sea. When they are
not frozen solid, they can also be hazardous to anyone trying to cross them. This potential
to both protect and hamper makes understanding the occurrence of slush-ice berms of
particular interest. Atkinson recognized that while these berm occurrences should be part of
an operational forecasting regime, no scientific work had been conducted on these
phenomena, and a physical model describing the formation of slush-ice berms during
storms did not exist. Eerkes-Medrano undertook this project, and established objectives and
methodology, with the intention of developing a physical conceptual model.
The nature of slush-ice berm formation precludes simple monitoring with an
instrument as is done, for example, with air temperature – there is no simple way to observe
this phenomenon. Slush ice berms are also episodic and spatially discontinuous, further
hampering their analysis. However, recognizing that local knowledge holders in Indigenous
communities live in a close relationship with the land and sea, and have a deep
understanding of their environment and its conditions – knowledge that is critical to their
survival – Eerkes-Medrano engaged local residents in Shishmaref, Gambell and Shaktoolik
to gather information and data on slush ice and slush-ice berm formation processes. The
aim was to develop a schematic/conceptual physical model of slush-ice berm formation
utilizing data gathered from these traditional knowledge holders. The following are the
6 1. Develop a conceptual model of slush-ice berm formation. This included:
a) Establishing a formalized nomenclature that represents the range of coastal
slush-ice berm types.
b) Identifying the synoptic weather conditions that led to these types of events
c) Examining the broader meteorological context in which slush-ice berms occur.
2. Document the specific traditional knowledge that was gathered for this project
concerning slush ice and slush-ice berm formation processes. This included:
a) Gathering and distilling this knowledge to identify the parameters conducive to
slush and slush-ice berm formation in the communities of study.
b) Collecting comments on the advantages and disadvantages that slush-ice berms
present for communities.
The intent was to examine the nature of the comments in their original form to
capture how raw community comments fed into the development of the physical process
model outlined in objective 1.
3. Describe the process by which traditional knowledge holders are engaged. This included:
a) Documenting the methods used to conduct interviews and to develop and build
trust.
b) Describing the tools used before and during the project to gather information to
bridge the cultures and narrow the gap that often exists between scientists and
local residents.
7 Traditional and Indigenous knowledge holders are those who maintain a cumulative
and dynamic body of knowledge based on a long history of interaction with the natural
environment and with each other. This knowledge is generally held collectively (UNESCO, 2006). Realizing the depth of knowledge possessed by these Indigenous and local experts, scientists working on the west coast of Alaska have increasingly engaged Inupiaq and Yupik
residents to examine and monitor natural processes. Their local observations and knowledge
have been very relevant in informing, guiding and complementing scientific studies that
aim to understand physical and environmental processes, and have resulted in scientific
contributions to hazard assessment and emergency response (Eicken, 2010).
In this project, Indigenous knowledge holders from Gambell, Shaktoolik and
Shishmaref were asked to identify specific dates and times of slush-ice berm occurrence
during the storms of 2009, 2011 and 2013. Once these specific dates were identified it was
possible to conduct the following:
Indigenous knowledge holders’ specific information on dates and times of event occurrence was complemented with information from the Sea Ice Zone
Observations Network (SIZONet/Eloka) database, which consists of
community-based observations by Indigenous sea-ice experts (SIZONet, 2008;
Apangalook et al., 2013; Eicken et al., 2014). The database also contains short
narratives on sea ice, weather and other significant features relevant to
residents. The information has been tagged by the SIZONet/Eloka staff for easy
access according to sea ice, weather, boating, and whale, polar bear, caribou,
and seal observation categories. The information can be filtered by observer,
8 communities of study and from the SIZONet/Eloka database, was then
interpreted, classified, and synthesized by the authors resulting in a
nomenclature that better represents the range of slush-ice berm formation
processes (Objective 1.a).
The chronology in which events occurred was relevant to conduct the synoptic weather analysis required to identify the specific weather conditions that led to
the formation of the slush-ice berm episodes of 2009, 2011 and 2013 (Objective
1.b).
Finally, based on local observers’ input and synoptic weather analysis, it was
possible to conduct an examination of the broader meteorological conditions
under which the various types of slush-berm formation occurred and to develop
a conceptual model of slush-ice berm formation (Objective 1.c).
The results of objective 1 are presented in Chapter 2, “Slush-Ice Berm Formation
on the West Coast of Alaska” (in press, journal Arctic).
The specific comments, descriptions and observations gathered from Indigenous
knowledge holders on slush and slush ice berm formation processes are presented in raw
form in Chapter 3. Inupiaq and Siberian Yupik Perspectives on Slush-Ice and Slush-Ice
Berm formation on the West Coast of Alaska (written as a manuscript to be submitted). This
approach was chosen to preserve and convey the insights and quality of the local knowledge
and to compare and contrast the knowledge held by residents in different communities. The
objective is to show how traditional knowledge is a type of science – based on hundreds of
years of observation required for the people’s survival – that can be interpreted from a
9 The methods used to engage Indigenous and local observers in this project are
documented in Chapter 4, Engaging Community and Stakeholders in Slush-Ice Berm
Formation and Impactful Weather Events Research in Alaska, USA (to be submitted). This
chapter presents the many issues and challenges encountered when engaging communities
and local observers in this kind of scientific research. It includes a description of the
preparatory work required before contacting communities, the approaches and tools used to
conduct interviews, and the challenges encountered during site visits including cancellation
of public meetings or the absence of interview participants who leave town to go hunting if
the day is good. Chapter 5, “Conclusion,” includes a summary of main results and
suggestions for future work.
1.1 Research Motivation
To understand the occurrence of a specific weather or sea ice phenomenon such as
the formation of slush ice and a slush-ice berm, and its impact on a specific community,
requires an understanding of the antecedent environmental conditions in the days up to and
during slush ice berm formation. Environmental conditions include air temperatures, wind
speed and direction, length and duration of the fetch of the wind, storm conditions, and
snow and sea ice conditions among others. In a place such as the western coast of Alaska,
this information is hard to obtain as weather stations are sparse and sometimes intermittent
(Cassano et al., 2011; McBean et al., 2005). Scientists, land managers and policy makers
trying to understand these events and their impacts do not have sufficient station data to
explore the climate drivers, and therefore they need to rely on different sources of
information. Working with traditional knowledge holders and local observers was the only
10 with the slush-ice and slush-ice berm formation episodes and in order to develop the
knowledge, nomenclature and conceptual model of slush-ice berm formation that will form
the basis for future research in this area and, eventually, the ability to forecast the formation
11 Figures:
Figure 1.1 Shishmaref: Abandoned house sits on the beach after sliding off during the 2005 fall storm. Credit: Diana Haecker/AP
Figure 1.2 Shaktoolik: Old power house.
Wire exposed in the old power house. Photo taken after the storm of November 9, 2013. Credit: Gloria Andrew
12 Figure 1.3 Shaktoolik: Concerns about drinking water quality.
View of town (left) and water intake infrastructure, first bend, Tagoomenick River (right). There is a concern about saline intrusion into the drinking water supply as the waves are able to reach the river, that supplies the town’s drinking water. Credit: USACE, BEA, 2009 (picture left), LEM 2013 (picture right)
Figure 1.4 Gambell: Airstrip.
13
2 Slush-ice berm formation on the west coast of Alaska
2.1 Article information
This chapter consists of a manuscript (in press) to be published in Arctic Journal.
Figures are the same as those submitted with the paper, but they have been renumbered for
consistency in this dissertation. References have also been reformatted for consistency.
2.1.1 Authors’ names and affiliations
*Laura Eerkes-Medrano1, David E. Atkinson1, Hajo Eicken2, Bill Nayokpuk3,
Harvey Sookiayak4, Eddie Ungott5, Winton Weyapuk, Jr.6
1Department of Geography, University of Victoria, Climate Laboratory. Department of Geography. P.O. Box 3060 STNC CSC, Victoria British Columbia, Canada, V8W 3R4
2Geophysical Institute, University of Alaska Fairbanks; International Arctic Research Center, University of Alaska Fairbanks, PO Box 757340, Fairbanks, Alaska 99775-7340
P.O. Box 757320, Fairbanks, AK 99775-7320, USA
3 Native Village of Shishmaref, P.O. Box 72110, Shishmaref, Alaska, 99772, USA
4 Native Village of Shaktoolik, P.O. Box 100, Shaktoolik, Alaska, 99771, USA 5 Native Village of Gambell P.O. Box 90, Gambell, Alaska, 99742, USA 6 Native Village of Wales,P.O. Box 549, Wales, Alaska, 99783, USA
14 2.1.2 Author’s and coauthors’contributions
Eerkes-Medrano developed project objectives and methodology to engage local
residents, conducted site visits and synoptic weather analysis, collected photographic
material, created figures and tables and wrote the manuscript. Atkinson edited figures and
reviewed and edited the manuscript. Eicken reviewed and edited sections of the manuscript
and facilitated access to the SIZONet database. Weyapuk has been a local observer and
regular contributor to the SIZONet database with observations on slush and ice formation.
Weyapuk, Nayokpuk, Ungott and Sookiayak provided information and reviewed sections
of the manuscript.
2.2 Abstract
Some coastal communities in Western Alaska have observed the occurrence of
“slush-ice berms”. These are features that form typically during freeze up when ice
crystal-laden water accumulates in piles on the shore. Slush-ice berms can protect towns from storm
surge, and they can limit access to the water. Local observations from the communities of
Gambell, Shaktoolik, and Shishmaref, and Wales were synthesized to develop a taxonomy
of slush-ice berm types and a conceptual process model that describes how they form and
decay. Results indicated two types of slush-ice berm formation processes: in-situ (forming
in place), and advective (pushed in by storm winds). Several formation mechanisms were
noted for the crystals that comprise in situ berms. Cold air temperatures cool the surface of
the water; crystal formation is aided by the occurrence of winds that translate surface
cooling through a greater depth. Snow landing in the water cools via melt of the snow and
the contribution of crystals directly to the water. A negative surge can expose the wet beach
15 Slush crystals for advective berm events form offshore. Winds move the slush towards shore
16
2.3 Introduction
Coastal western Alaska, defined for this study as the northern Bering and southern
Chukchi Sea between the Yukon-Kuskokwim Delta and the area just north of Bering Strait
(Fig. 2.1), is home to numerous villages and several larger hub communities. Almost all of
these communities are situated on the coast, and in some cases on sand or gravel bars – a
necessity imposed by transport and subsistence needs, which include low, flat ground for
airstrips and access to the water for hunting and fishing and to receive sea-lift barges. This
region experiences annual sea-ice cover formation, which, at its maximum extent, reaches
well south into the Bering Sea (Fig.2.1). In recent decades the sea-ice cover has been
forming later in the fall. This has lengthened the ice-free season, resulted in a less stable ice
cover and has exposed increasingly larger areas to storm impacts (Frey et al., 2014; pers.
comm. with Shaktoolik residents, 2013).
Coastal western Alaska sees regular incursions of storms moving up from the
western North Pacific, a spur off one of the most active storm tracks in the Northern
Hemisphere, which stretches across the North Pacific Ocean from regions off eastern Asia
to the northeast towards the Aleutian Islands and Gulf of Alaska (Mesquita et al., 2010).
Often when storms reach these regions they are in the mature phase of their life cycle and
their potential for peak impact is slowly weakening. Storms that move into the seas off
western Alaska can stall, remaining stationary for days, resulting in moderate to strong
winds blowing from the same direction for extended periods of time. In some cases,
however, when upper air conditions are favorable, these storms can re-energize. The
resultant strong winds from slow-moving, long-duration weather systems, when combined
17 water-level surges of as much as 3 m into shallow coastal areas (Chapman et al., 2009;
Terenzi et al., 2014; Erikson et al., 2015). Surges and wave action cause inundation and
erosion that damages both infrastructure and subsistence forage areas (e.g., berry-picking
areas), and can cut-off communities.
Sea ice too can cause major damage. Atkinson et al. (2011) described an incidence
of severe damage to a local cannery in the Bristol Bay area which occurred as a result of
storm surge acting upon ice that had formed on the structure’s wharf facility. However, sea
ice can also protect communities from surge and wave action in several ways. Large pieces
of floating ice dampen wave energy and prevent the wind transfer of energy into the water,
and land-fast ice armors the coast increasing its resistance to erosion (Eicken et al., 2009;
Atkinson et al., 2011). In the early sea-ice formation stages, frazil or slush ice can be driven
onto shore and pile up in the nearshore area by storm winds. If slush ice accumulating on
the beach has an opportunity to consolidate through in situ freezing, it may form solid
defensive structures and can greatly limit the adverse impact of surges, as has been
witnessed by local ice experts and residents in communities such as Unalakleet, Shishmaref
and Wales (Eicken, 2010; Eicken et al., 2014). In 2009 a storm threatened Shaktoolik and
other communities at the eastern end of Norton Sound with floods from an anticipated storm
surge. However, slush ice was driven ashore, solidified, and formed a natural defensive
barrier (a “berm”) that mitigated storm surge impact (observations from the community as
reported in USACE 2011). Similar findings have been reported for the Bering Strait region
(Eicken et al., 2014). In Shishmaref, where key infrastructure is threatened by coastal
erosion (GAO, 2009), and where ice threatens the integrity of engineered revetments put in
18 impacts. Once solidified, slush-ice berms can also impede travel and access to the sea and,
in an unfrozen state, be hazardous to anyone trying to cross them. This potential to both
protect and hamper makes understanding the occurrence of slush-ice berms of particular
interest.
While slush ice and berm formation are part of the traditional knowledge system of
indigenous ice experts and residents of coastal communities in western Alaska, the topic
has been addressed only a few times in scientific literature and reports. Slush ice in the
coastal zone has been studied by Wiseman (1973) and Reimnitz and Kempema (1987).
More recently, a post-storm analysis of the November 2011 strom provided detailed
descriptions of berm formation in the coastal zone, but the intent of the report was not to
analyze causal mechanisms for the berms (Kinsman and DeRaps, 2012). These studies did
not provide a detailed breakdown of the weather controls that need to be in place for its
formation. To address this, we undertook a study that combines analysis of eight years of
ice observations by Inupiaq and Yupik experts with field visits to gather traditional
knowledge and local observations of slush and slush-ice berm formation in three
communities: Shishmaref, Shaktoolik, and Gambell. Our goal for this paper was to develop
a conceptual model of slush-ice berm formation based on observations and comments
provided by local experts, as supported by an analysis of the synoptic weather conditions
and the meteorological context that lead to these types of events. Specific elements of the
traditional knowledge on slush ice and slush-ice berm formation gathered for this project
will be presented in a separate paper.
19 2.4.1 Study sites
Three communities – Gambell, Shaktoolik, and Shishmaref – were locations that
were visited by some of the authors for this particular project. Although not visited, Wales
is included because it has numerous entries in the community observation database called
the Seasonal Ice Zone Observing Network (SIZONet), which provided additional useful
observations and examples.
Gambell is a community of 681 people (U.S. Census Bureau, 2010), situated on the
northwest cape of St. Lawrence Island, 200 miles southwest of Nome. The community is
on a gravel spit which is constantly moved by waves and currents. Gambell’s nearshore
environment is categorized in this paper as “deep,” which means it slopes rapidly down,
reaching a depth of 30+ m at 6 km from shore. It has a small tidal range, approximately
0.5m between high and low tide. The spit is periodically eroded along the north and west
shorelines by storm-generated waves (USACE, 2008). The isolation of Gambell has helped
residents maintain their traditional St. Lawrence Yupik culture, their language, and their
subsistence lifestyle, which is based on marine mammals. Gambell subsists largely on
harvests from the sea -- seal, walrus, fish, and bowhead and gray whales (Gambell, 2012).
Shaktoolik is a community of 251 people (U.S. Census Bureau, 2010) situated near
the north end of a sandspit in Alaska’s Norton Sound. Shaktoolik has a “shallow”
beachfront, reaching only ~6 m at 6 km distance from the coast. Shaktoolik has a slightly
larger tidal range than Gambell or Shishmaref, approximately 1.5 m. With the Tagoomenik
River to the east and Norton Sound to the west, the community has water on two sides. The
community has been relocated twice, once in 1933 and again in 1967 because these sites
20 local economy is mixed, based on commercial fishing, traditional subsistence activities, and
local jobs (Shaktoolik, 2013).
Shishmaref is a community of 563 people (U.S. Census Bureau, 2010), located on
Sarichef Island along the northern coast of Seward Peninsula on the Chukchi Sea.
Shishmaref is also a shallow beachfront, also reaching ~7 m at 6 km from shore. Shishmaref
also has a small tidal range of approximately 0.5 m. The Island is exposed to severe fall
storms. In this community, as many others on the west coast of Alaska, state flood disaster
declarations have been issued in 1988, 1997, 2001, 2002, 2005, and 2011 (Alaska
Department of Military and Veterans Affairs [ADMVA], 2008; Parnell, 2011). According to
Kawerak (2012) the bluff on the north shore of the island erodes at an average of one to
one-and-a-half meters a year. Several engineered structures have been built to lessen
shoreline erosion (Mason et al., 1998). However, there are no engineered flood protection
measures in place (FEMA, 2009). It is a traditional Inupiat Eskimo village with a fishing
and subsistence lifestyle (Shishmaref, 2012).
Wales is a community of 145 people (U.S. Census Bureau, 2010), located near Cape
Prince of Wales defining the eastern boundary of Bering Strait. The village is located in
low-lying areas of unconsolidated sediments below Cape Mountain; its nearshore zone may
be categorized as deep, reaching ~40 m at a distance of 6 km from shore. Wales also has a
small tidal range of approximately 0.7 m. Strong winds and currents result in dynamic ice
conditions beyond a narrow belt of shorefast ice forming in December or January
(Weyapuk, in Apangalook et al., 2013). It is a traditional Inupiat Eskimo village with a
21 Observational data about slush ice berm occurrence were obtained from two
sources. The first consisted of dedicated site visits to the communities of Shishmaref,
Shaktoolik, and Gambell. Two site visits were conducted in each community. Visits to
Shishmaref took place in August and October 2013. Visits to Gambell and Shaktoolik
occurred in November 2013 and August 2014. The November 2013 visit was particularly
well timed because a strong storm was in progress at the time, which afforded an
opportunity to observe the process of berm formation first-hand. During the first visit, five
semi-directed interviews with local observers were held to gather information about
slush-ice berm event occurrence and the environmental context of their formation, including
specific dates. Interview data consisted of raw written notes and audio recordings from the
interviews. Discussions with community members also resulted in the acquisition of
photographs. All raw interview data were reduced by an initial hand transcription followed
by a search through the transcribed notes and other sources for information of relevance to
berm occurrence. During the second visit to Shaktoolik and Gambell, the five interviewees
were also asked to comment on photographs taken by the authors of the in-situ slush-ice
berm formed in November 2013, and on photographs taken by residents, of the advective
slush-ice berm formed during the storm of 2009.
The second source consisted of an existing database of community-based
observations by indigenous sea-ice experts established by the Seasonal Ice Zone Observing
Network (SIZONet; Apangalook et al., 2013; Eicken et al., 2014). The database holds a
large number of near-daily observations, for several communities along the west coast of
22 indigenous sea-ice and environmental experts from the respective communities recording
ice and weather conditions relevant to local uses of the ice cover and associated hazards.
Specific dates for berm occurrence were important and came from observations and
interviews, and guided the analysis of the synoptic (weather) patterns that prevailed for the
periods preceding, during, and following berm occurrence. Data concerning weather
patterns was obtained from an online portal and tool system maintained by Earth Systems
Research Laboratory (ESRL), operated by the US National Oceanic and Atmospheric
Administration (NOAA). This site uses “reanalysis” data – grids of weather variables
generated by weather forecast models run for past time periods using observational data
available at those times – and a selection and display portal that allows the user to easily
plot variables of interest. Two specific reanalysis datasets were used: NCEP/NCAR global
reanalysis (Kalnay et al., 1996) for rapid, general assessment and, when more detail was
required, the higher-resolution North America Regional Reanalysis. Maps of pressure,
wind, and temperature parameters were produced and then qualitatively analyzed to look
for explanatory patterns. The NOAA/ESRL portal may be found at
http://www.esrl.noaa.gov/psd/data/composites/hour/. After initial analysis of community
observations and weather information, a second visit to each community took place to
present the findings to the community, to ensure veracity and obtain feedback from them.
23 2.5.1 Types of Berms
Three types of berms were identified – based on mode of formation – that can protect
communities from storms and are relevant in the context of coastal dynamics: 1)
shoved-ice – non-slush berms consisting of slabs and boulders of shoved-ice piled up through an shoved-ice shove.
Because this is not a slush-ice berm, it is only mentioned briefly as it is the first type of
berm that come to residents’ mind; 2) in-situ slush-ice –berms consisting of slush ice formed
in place and/or freezing of seawater in exposed parts of the beach; and 3) advective
slush-ice –slush-slush-ice berms composed of slush slush-ice, frazil and/or small slush-ice aggregates moved in
from somewhere else. The most essential condition for slush-ice berm formation (whether
in-situ or advective) is water temperature that is at or below the freezing point (-1.8°C for ocean waters in the region). Note that we are distinguishing between ice berms based on
mode of formation, rather than berm structure. This approach is in line with the goals of
this study, relating specific environmental conditions to formation of ice berms. A
classification based on structure would cut across the different formation modes, and would
need to differentiate berms in terms of the size of individual aggregates (e.g., frazil grain,
aggregated slush flocs, ice gravel, ice block, ice raft).
Shoved-ice Berms: Shoved ice is the most common type of berm mentioned by
people in the communities. This type of berm forms when well-established sea ice is driven
ashore by wind and/or currents (Mahoney et al., 2004), can form very rapidly, reaching a
height of up to 10 m to 13 m, and can form “anywhere” when the conditions are right during
the fall season (Eddie Ungott, pers. comm., Gambell, November 2013; Roy Ashenfelter,
24 occur later in the season when the offshore ice pack is compact enough to transmit stress
over longer distances (Mahoney et al., 2004). This type of berm is not the subject of this
study, but is mentioned here to make the distinction clear.
In-situ slush-ice berms: These berms form primarily on the beach closest to the
water under appropriate conditions of air and water temperature, wind, and wave
conditions. A berm can form in a matter of hours in response to air and water temperatures
below freezing (typically below –1.8°C for ocean waters in the region). The height of
in-situ type berms is usually no more than 1 m and is determined by wave splash height. Berm
width is determined by the distance between the high and low tideline, in the following
manner. After a drop in air temperature, at low tide the beach is exposed to cold air which
allows ice crystals to form in interstitial water and at the surface of beach sediments. As the
tide moves in, the water picks up the crystals which form an ice crystal water slurry, termed
slush, and builds successive berms culminating with a relatively large berm at the high
tideline. As the tide goes out, it continues piling berms until it reaches the low tideline (Fig.
2.2). Community observations also indicate that the slush ice accompanying the berm can
extend up to roughly 1.5 km offshore, depending on weather conditions. This occurs under
the persistent action of waves, which continues to push slush towards the shore. When the
slush associated with the berm extends offshore to a distance of 0.5 km or more wave action
is attenuated, reducing wave energy at the shore. The in-situ berm formation process can be
accelerated by snow falling on the water: melting of the snow can increase the rate of
cooling of the water, and the introduction of ice crystals provides nuclei onto which larger
25 1978). Once the in-situ berm has reached a certain height and width and is large enough to
remain in place, if the winds intensify and waves spill onto and over the berm the water will
freeze when it comes in contact with the berm, creating a solid surface; but the interior of
the berm will still remain unfrozen until enough time has passed for it to solidify completely.
Community residents related their observations that slush-ice berms form faster in
areas where the nearshore coastal environment is shallow, such as at Nome. They noticed
that, as the waves break close to the shore (surf zone), the water continues moving up on
the sloping beach and, if it is cold, when the water recedes (backwashes) it will start to form
ice crystals (slush) on the beach. When exposed to cold air the beach cools enough that it
can rapidly freeze the water that washes over it during successive waves. In addition, slush
will also begin to form in the shallow surf zone. When the waves come in, they lift the ice
crystals from the beach and push this, along with the slush in the surf zone, onto the beach
where it will start to accumulate forming a berm. Each successive wave brings a new slush
deposition, increasing the berm’s height and thickness, and the berm continues to form as
long as there is wave action. A drop in sea level – negative surge – will enhance the
slush-ice berm formation process by exposing more water-saturated beach to cold air.
Along deep coastal areas, such as those near Gambell, residents observed that slush
takes longer to form and slush-ice berm formation starts only when the water is cold and a
large number of crystals form in the nearshore zone, giving surface waters the consistency
of “oatmeal” (a mixture of water and ice crystals). This ice in the water will rise to the
surface, and if the slush layer is a few centimeters thick, it is able to dampen smaller waves
and breakers, which reduces the movement of slush towards the shore. Therefore, waves of
26 inertia conferred by the presence of the slush layer and lift the slush up and push it to the
shore, where it will start piling up. As with the in-situ berm, each subsequent swell will
continue the process of piling the slush onto the shore.
Three examples of in-situ slush ice berm formation and their associated weather
context are presented. Two occurred in Wales – the first on 8 November 2007, and the
second on 10 November 2012 (based on observations by Weyapuk, in Apangalook et al.,
2013) – and the third occurred in Shaktoolik on 15 November 2013 (L. Eerkes-Medrano,
pers. obs.).
Observations of the ice berms formed at Wales are limited to indications of physical
dimension. Wind analysis for the first two events show a general east/north easterly
direction and speeds of about 4 to 8 m/s. Both events are associated with a low-pressure
system over the Aleutian Islands (e.g. Fig. 2.3). The position of this low explains the air
flow direction, indicating that the low pressure system was drawing relatively cold
continental air from over the Alaska mainland to the east, resulting in a reduction of
temperatures in the vicinity of Wales. In the day leading up to the slush ice berm formation
events air temperatures of approximately –3 °C to –4 °C dropped to approximately –8 °C over a period of about a day as the low pressure systems moved in (Fig. 2.4). In both cases,
Weyapuk reported an associated slush-ice zone extending for over 0.4 km from shore.
The in-situ slush-ice berm started to form on the beach, along the low-tide line, on
15 November. The observed mean maximum temperature that day was –7 °C and the mean
minimum –11 °C. Temperatures in this range continued during the week. Community
members mentioned that 15 November was the first day of cold weather after a series of
27 of slush-ice berm formation. The berm disappeared in the afternoon, when the temperature
rose, and it formed again the next day. This diurnal cycle of formation and decay continued
for the next three days; on the fourth day, two slush-ice berms had formed parallel to each
other – one along the low-tide line and one along the high-tide line. Slush had also
accumulated between these two berms and was starting to solidify (Fig. 2.2). There was
also slush offshore extending for about 200 m. Winds during this event were moderate out
of the north/northwest. Unlike the first two events described, this event was not associated
with a low pressure system but rather a general pressure pattern that favored a northerly
flow (Fig. 2.5). Despite different causes, these weather conditions are similar to those
observed during the first two events discussed above: low to moderate wind speeds (< 8
m/s) bringing weak wave conditions and temperatures dropping to approximately –8 °C/–9 °C.
Advective ice berm: The essential process distinguishing an advective
slush-ice berm type from the in-situ type is that the slush is moved in from elsewhere – advected
– by strong winds or onshore currents.
Reimnitz and Kempema (1987) observed large volumes of slush-ice forming during
storms in the shallow areas of the Beaufort Sea. They theorized that during these storms, a
large quantity of heat is removed from the surface water in a very short time, facilitating
the formation of a large volume of slush ice, consisting of frazil ice crystals from 1 to 5 mm
in diameter (Martin,1981), that rises to the surface. Reimnitz and Kempema (1987) refer to
the sea turning into “applesauce” during these storm episodes. Because of the constant
28 ice cover, is uncommon. This slush production was observed to occur only when the wind
velocity was at least 10 m/s and the air temperature about –10°C or less. The thickness of
the water-saturated slush can range from a few centimeters to several meters; when the
storm subsides, the slush freezes from the surface down, slowing or stopping wave motion
(Reimnitz and Kempema, 1987). Once the slush solidifies, it usually breaks again due to
tension or shearing, resulting in geometric ice shapes which are pushed by the waves and
currents against the shore (Morecki 1965; Reimnitz and Dunton, 1979). During the strong
2009 storm in Shaktoolik that resulted in a large berm, residents observed that the
temperature was not cold at the time of the storm, that slush was not present in the water
before the storm, and that they had no idea where the slush came from; it was snowing and
the sea conditions were very rough. After the storm residents observed bands of crushed
slush/frazil ice aligned obliquely to the beach, indicating compression by wave fronts (Fig.
2.6). These observations from Shaktoolik support the idea of rapid heat loss, suggested by
Reimnitz and Kempema (1987), and the solidification process suggested by Morecki
(1965), and Reimnitz and Dunton (1979). In Gambell, residents also mentioned that when
there is a fall storm, the slush-ice berm forms immediately, and that as long as the wind
continues to blow, the accumulation continues to grow and solidify. If the wind-driven
motion is directed offshore, the slush will be blown away from the beach.
Slush-ice moves with the wind- and current-driven surface water until it is piled up
against stationary ice or land (Reimnitz and Kempema, 1987). If pushed against sheets of
solid ice the slush ice will be driven down and can accumulate to a thickness of more than
29 anchor-ice “ice boulders,” rises to the surface, where it can mix with snow and slush ice,
and it can be pushed against the beach (Reimnitz and Kempema, 1987). Reimnitz and
Maurer (1979) mention ice “boulders”, or wide, flat pans up to 5 m in diameter being
deposited along the Alaskan Beaufort Sea coast during a westerly storm in September 1970.
Short and Wiseman (1974) noted that on Pingok Island, after a late fall storm, ice pans less
than 10 m in diameter and 60 cm thick piled up on the shore along with the slush-ice, but
these formation episodes varied in time and place and from year to year. In years without
fall storms, such as 1971 and 1985, Reimnitz and Kempema (1987) did not notice the
production of large amounts of slush/frazil, but during the fall storm of 1978, the slush-ice
berm was 4 m thick.
Similar observations were noted by residents in Shaktoolik during the fall storms of
2009, 2011, and 2013. During the advective slush-ice berm formation episode of 2009,
residents mentioned that two berms formed in town. In the first part of the storm episode,
the storm surge accompanied by strong wave action pushed the slush ice farther back from
shore, onto the shallow part of the beach (in front of the town), to a height of more than 3
m. When the winds subsided, the swells continued to pack the slush against the beach. A
few hours later, the wind picked up and the storm surge pushed more slush-ice onto the
shallow beach and in front of the old town, where the beach is only slightly deeper than in
front of the new town. There it formed an advective slush-ice berm higher than 4 m and
deposited large, thick ice pans on the beach, forming a wall (Fig. 2.7). Residents noted that,
during the 2009 episode, fall temperatures had been relatively warm before the storm, that
the advective slush-ice berm formation was a result of the storm, and that it was snowing
30 protected by an advective slush-ice berm but there were no large pieces of ice. During the
2013 storm no slush-ice berm was formed.
In Gambell and Shaktoolik residents mentioned that snow and blizzards accelerate
the advective slush-ice berm formation process. Osterkamp (1978) mentioned that if it starts
to snow heavily, the introduction of snow into the water will aid ice crystal growth as
mentioned previously. Under the right conditions, the ice nuclei grow rapidly but are broken
up by flow turbulence and collisions (Martin 1981). The broken pieces act as secondary
nuclei for the formation of more ice crystals, and large amounts of slush ice are produced
very quickly (Kempema et al., 1990).
Synoptic weather patterns
The NCEP/NCAR reanalysis data for these events reveal the following:
During the 2009 and 2011 episodes, an advective slush-ice berm formed during
periods of intense storm activity resulting from a low-pressure system located in the Bering
Sea, just to the west of Norton Sound (Figs. 2.8 and 2.9). In both cases, the location of the
low-pressure system resulted in west and southwest winds at Shaktoolik, driving waves and
slush directly onto the beach. The wind speeds during the 2009 storm were about 14 m/s
with gusts of up to 22 m/s, and during 2011 the winds speeds were reaching 18 m/s with
gusts of up to 39 m/s (Figs. 2.10 and 2.11). In both events, during the 10 days prior to the
storms, temperatures ranged between –5 °C and –10 °C. On 11 November 2009, and 9 November 2011 – the days when the storms hit – the temperatures were about –8 °C and – 9 °C, respectively (Figs. 2.12 and 2.13). These two storms may be contrasted with another storm that occurred on 9 November 2013, which did not produce a berm. During this event
31 the air temperatures were above 0 °C, and during the storm episode the air temperatures were 2 °C (Fig. 2.14), not enough to cool the water to produce slush. Although the pressure system was west of Norton Sound, it covered a much larger area than the
low-pressure systems of 2009 and 2011 and extended from Bristol Bay to the Chukchi Sea (Fig.
2.15). The greater width of the storm meant that the wind direction was from the south and
southwest, instead of from the west, and not so directly facing Shaktoolik.
Advective slush-ice berms form in the presence of onshore winds. The particular
form they take is determined by two additional environmental conditions – air temperature
and presence of a storm surge – that can combine to result in four possible advective
slush-ice berm forms.
The first condition, storm surge and cold air, can result in the formation of large
advective slush-ice berms farther inland from the shoreline (Fig. 2.16). This type of berm
usually forms above the normal high-water mark, is mostly solid, and is higher than about
3 m. It can protect a village from storm action. Once it forms, it solidifies and may remain
in place for the duration of the winter.
The second condition, no storm surge and cold air, results in an advective slush-ice
berm of moderate height, about 3 m or less, forming near the shore. Because it forms in
cold air and with wave action, the resulting berm is quite strong, durable, and larger than an
in-situ berm. Note, that in the Bering Strait region moderate height berms are typically less
than 1 m high because of significantly smaller fetch and different nearshore bathymetry that
32 The third condition, storm surge but no cold air, results in a large, wide advective
slush-ice berm that is dangerous to walk on because the air is not cold enough for the berm
to be frozen thoroughly. A person can fall through when attempting to walk on it. Residents
of Gambell mentioned that with this type of berm, the more a person moves, the deeper and
deeper they sink into it, because the slush-ice is like quicksand.
The fourth condition, no storm surge and no cold air, results in an advective
slush-ice berm of moderate height, not frozen solid and therefore also not strong enough to walk
on safely. As with the previous type of berm, a person can sink while attempting to walk on
it.
For both in-situ and advective slush-ice berms, if they form under conditions of
warm air (above 0 °C) they will remain in a slushy state; they will be solid enough to remain
in place but not to support the weight of a human. If no subsequent wave or surge event acts
to melt them, as the air temperatures decrease these berms eventually solidify.
In-Situ Berm Conditions: An issue that came up during this study is the role of beach characteristics in the formation situ slush-ice berms. In the shallow coastal areas, the
in-situ slush-ice berm will form as long as there is slush in the surf zone; it will be washed
onto the beach and deposited along the low or high tideline, where it can further develop.
Along beaches with a steeper profile, community residents mentioned that swell must be
occurring in order to push the slush onto the beach. The role of temperature is also identified
–if the temperature is too low and there is no wave action, the beach surface may freeze,
forming a solid crust, and no slush-ice berm formation will occur. These observations point
33 study: slope of beach and nearshore zone, as well as the sediment grain size. The steeper
gravel beaches of St. Lawrence Island and parts of the North Slope of Alaska exhibit
different wave run-up characteristics and because of higher permeability of beach sediments
and larger grain size are less likely to form surface ice crusts.
Synoptic weather analysis of in-situ slush-ice berms corroborates the community
observations that they can form “very rapidly” if there is a rapid drop in temperature. During
the days prior to the in-situ slush-ice berm formation in Wales (8 November 2007, and 10
November 2012) and Shaktoolik (15 November 2013), the temperatures had been above
0°C, and as soon as temperatures dropped below 0°C the berms formed. The SIZONet database shows that several other episodes of small in-situ slush-ice berm formation and
disappearance took place every year between 2006 and 2014 during the fall in Wales,
Barrow, and Gambell. A total of 53 daily observations out of >5000 reference slush-ice
berm formation in these communities for the specified time period. Most of these episodes
were observed in Wales, but they were not considered in more detail here because they were
too small to protect the town from a storm. However, a cursory synoptic weather analysis
suggests that there is no particular association of these smaller events with low-pressure
systems, but rather to a general cooling of temperatures associated with the fall season.
Also, in Wales, the beach is wider than at Gambell or Barrow, which corroborates
observations from residents of Shishmaref that the in-situ slush-ice berms formed when
there was a sizable beach; in Shishmaref, now that the beach has been eroded, a slush-ice
berm does not form. In Gambell, it was mentioned that slush-ice berms form faster on
34 If the temperature remains low, the berms in shallow water solidify more rapidly and as a
result are safer.
Advective Slush-Ice Berm Conditions: An analysis of the synoptic weather
conditions that produced an advective slush-ice berm in Shaktoolik during the storms of
2009 and 2011 reinforces Reimnitz and Kempema (1987) observations as follows. First, the
occurrence of strong winds (> 10 m/s) from an onshore direction allows large wind-driven
waves and causes the slush in the nearshore/offshore zone to be pushed directly onto the
beach. Second, conditions of low air temperature are important insofar as durable slush-ice
berms were only observed at temperatures below –10 °C. Third, the occurrence of snow provides crystals for nucleation and aids in cooling of the surface water layer (Osterkamp,
1978). It was snowing during both of the advective slush-berms episodes in Shaktoolik; in
both cases as well the wind speed was well above 10 m/s (14 m/s in 2009 and 18 m/s in
2011), and the air temperatures, were about –10 °C. The observation by Osterkamp (1978) of the contribution of snow in seeding the water and accelerating the slush formation
process was corroborated by residents in all three communities. One additional community
observation is that the weather patterns conducive to the formation of an advective
slush-ice berm are very limited and site-specific. Short and Wiseman (1974) and community
observers have mentioned that this process takes place in a very short period of time when
the conditions are adequate.
